Lubricating systems for internal combustion engines are known. In certain known lubricating systems, a lubricating oil drops to a basin at a bottom portion of a crankcase housing after lubricating one or more portions of the internal combustion engine. The recovered oil is then fed through an oil cooler where thermal energy is removed from the oil and the cooled oil is fed to an oil filter. After passing through the oil filter, the cooled oil is again introduced to the one or more portions of the internal combustion engine in need of lubrication. The oil then drops back to the basin, thereby completing the oil circuit for cyclical use.
In certain known oil lubricating systems, such as the one described above, oil pump output capacity, by design, significantly exceeds lubricating demand under most, if not all engine operating conditions and speeds. To prevent an excessive build-up of pressure (and resulting pump or other components damage) when oil supply exceeds oil demand, a pressure relief valve is provided in the oil circuit immediately downstream of the oil pump and upstream of all other lubricating system components, including the oil cooler. Thus, if the oil pressure within the oil circuit builds up at the position of the pressure relief valve, the pressure relief valve will open, thereby alleviating the pressure by discharging the oil back into the oil reservoir in the basin. Pressure buildup can occur, for example, during engine startup when the oil is cold and has increased viscosity, in instances where the oil filter or other part of the oil circuit become blocked/clogged, and during most, if not all engine operating conditions when pump output exceeds lubricating oil requirements of the engine. Thus, the pressure relief valve provides a mechanism by which the excessive pressure within the oil circuit is eliminated by dumping the oil back into the oil reservoir.
During engine cold start conditions, because the oil is dumped back into the oil reservoir prior to flowing through the oil cooler, the temperature of the oil in the oil reservoir will build up faster when the pressure relief valve is an open state. However, since the pressure relief valve never returns to the fully closed state once normal engine operating conditions are reached, the oil may not be adequately cooled prior to being reintroduced to the portions of the internal combustion engine in need of lubrication.
Thus, a need exists for a lubricating system for an internal combustion engine that can both relieve oil pressure within the oil circuit as needed while at the same time increasing the amount of thermal energy removed from the oil.